This invention relates to a technique for suppressing arcs in an electromagnetic waveguide, and more particularly to a passive technique that introduces vent holes at a high point in a waveguide run.
Waveguides have been used for some time as an efficient way to carry microwave frequency energy over distances in a predictable manner. However, waveguides in some instances have a tendency to experience unpredictable behaviors such as internal arcing. In particular, even though a waveguide is sized to be capable of operating safely at the expected power levels without introducing a voltage breakdown, certain events or faults may occur to cause an energy discharge within the waveguide itself. Such faults may happen when dust, dirt or other ambient conditions introduce an abnormal voltage condition inside the waveguide. Such arcing is of concern since it may actually continue after the fault is no longer in existence. The arc not only partially blocks transmission of energy through the waveguide, but also may damage other system components.
For example, electromagnetic energy normally travels within the waveguide from an electromagnetic energy source through the waveguide towards a system that makes use of the microwave energy, such as a microwave oven cavity. Once an arc occurs, it tends to travel backwards within the waveguide, back towards the power source. The arc acts to reflect at least some electromagnetic energy back to the power source. This causes a decrease in power levels at points in the waveguide beyond the arc, meaning that the system in turn receives electromagnetic energy at a reduced power level.
A number of methods have been used in the past to detect and deal with the occurrence of an arc within a waveguide. For example, detectors may be attached to the waveguide which are responsive to the vibratory and electromagnetic disturbances resulting from an arc. The detectors can be arranged not only to determine the existence of an arc but also its location and velocity.
Upon detection of an arc, electronic control circuits can then be used to shut off the microwave power source or reduce its level so that the arcing will eventually cease. After a suitable delay, to allow any ionization caused by the arc within the waveguide to dissipate, the power source is then brought back on line again.